1. Field of the invention
The invention in general relates to battery chargers and more particularly to a high power, pulsed current battery charger system particularly well adapted for the rapid charging of electric vehicle batteries.
2. Description of related art
After a predetermined use, a secondary battery may be recharged by supplying a charging current until full battery charge is restored. In one typical system, charging current is supplied by a source of ac power connected to a rectifier which then provides dc current to the battery for a certain time period depending upon the battery state of charge.
In an improved battery charging technique, the charge profile consists of one or more positive charge pulses of relatively long duration, followed by one or more negative discharge pulses of relatively shorter duration. This alternate charge-discharge pulse technique enhances battery charge acceptance, reduces internal heating, reduces the time necessary for battery charging and prolongs battery life.
In some battery systems, such as utilized in electric vehicles, a string of batteries provides operating potential of hundreds of volts at a current rating of hundreds of amperes. These high power battery systems are typically charged from a high voltage multiphase power line. It would be desirable to charge these high power batteries utilizing the alternate charge-discharge pulse technique. The problem however is in devising a relatively low cost system which will provide satisfactory pulse characteristics while maintaining the quality of the ac input power in terms of power factor and harmonic distortion of the ac current. The present invention provides a solution to the problem.